Two-component or multi-component injection molding procedures are known from the art of plastic processing. Illustratively reference is made to Ch. Jaroschek, “Das Mehrkomponenten-Spritzgiessverfahren' [Multi-component injection molding”] in Swiss Plastics 19 [1997] #12 or to U. Stenglin “Hart/Weich-Verbindungen und anwendungsbezogene Modizifierbarkeit von TPE-S (SEBS/SEPS)” [Hard/soft compounds and application-specific modification of TPE-S (SEBS/SEPS), Swiss Plastic 20 [1998] #3. These sources elucidate the advantages of two- or multi-component injection molding with respect to costs of tools, personnel, machinery and materials. These methods basically are categorized into sandwich molding injection and overmolding procedures. If not exclusively but primarily, the interest herein is the cited overmolding method. In this procedure a part is manufactured from a first material component and it is then overfilled at least segment-wise with a second, different material component, the second part of a different material being built-up on the said first part. All sprayable thermoplastics can be used, in particular also for overmolding, and furthermore, even if in very special applications, also further materials which cannot be joined.
The above cited costs obviously also represent substantive production factors in the manufacture of hearing aids. But with respect to the manufacture of hearing aids, there is additionally the problem of space because a permanent requirement of this field is always the most compact possible design.